U.S. patent number 6,764,643 [Application Number 10/054,954] was granted by the patent office on 2004-07-20 for powder compaction method.
Invention is credited to Hiroshi Nagata, Masato Sagawa, Tochihiro Watanabe.
United States Patent |
6,764,643 |
Sagawa , et al. |
July 20, 2004 |
Powder compaction method
Abstract
A powder compaction method in which a powder p is filled by air
tapping or other suitable method into a mold 1, then while the mold
1 being filled with the powder, the powder particles are bound with
each other without application of force from outside the mold to
form a compact C, and then the compact C is taken out from the mold
1. This method produces a variety of shapes of the compact far
greater than in conventional methods, and net shape manufacturing
of products with complex shapes is made possible by this method.
Because this method uses far less binder compared to MIM and PIM
that are expected as methods for producing products with
complicated shapes, the time needed for elimination of the binder
is much shorter than in MIM and PIM.
Inventors: |
Sagawa; Masato (Kyoto,
JP), Watanabe; Tochihiro (Kyoto, JP),
Nagata; Hiroshi (Kyoto, JP) |
Family
ID: |
27335709 |
Appl.
No.: |
10/054,954 |
Filed: |
January 25, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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474813 |
Dec 29, 1999 |
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404229 |
Sep 23, 1999 |
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Foreign Application Priority Data
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Sep 24, 1998 [JP] |
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H10-269273 |
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Current U.S.
Class: |
419/2; 419/36;
419/37; 419/38 |
Current CPC
Class: |
B30B
11/00 (20130101); B30B 15/302 (20130101) |
Current International
Class: |
B30B
15/30 (20060101); B30B 11/00 (20060101); B22F
001/00 () |
Field of
Search: |
;419/38,2,36,37 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Jenkins; Daniel J.
Attorney, Agent or Firm: Morrison & Foerster LLP
Parent Case Text
This application is a continuation of Ser. No. 09/474,813, filed
Dec. 29, 1999, now abandoned, which is a continuation in part of
Ser. No. 09/404,229, filed Sep. 23, 1999, now abandoned.
Claims
We claim:
1. A powder compaction method, comprising: filling a powder into a
mold by air tapping, binding the particles of said powder to each
other without application of force from outside the mold after the
mold is filled with said powder to form a powder compact, and then
removing the powder compact from said mold.
2. A powder compaction method according to claim 1, further
comprising adding a binder to the powder to be filled.
3. A powder compaction method according to claim 1 or 2, further
comprising adding a lubricant to the powder to be filled.
4. A powder compaction method according to claim 1 or 2, in which
the binding of the powder particles is carried out by a heat
treatment within the mold.
5. A powder compaction method according to claim 3, in which the
binding of the powder particles is carried out by a heat treatment
within the mold.
6. A powder compaction method according to claim 2, in which the
binding of the powder particles is carried out by a chemical
reaction within the mold.
7. A powder compaction method according to claim 3, in which the
binding of the powder particles is carried out by a chemical
reaction within the mold.
8. A powder compaction method according to claim 2, in which the
binder is present in an amount of 4 to 20 volume % of the powder
particles.
9. A powder compaction method according to claim 3, in which the
lubricant is present in an amount of 0.5 to 14 volume % of the
total powder particles, binder and lubricant.
10. A powder compaction method according to claim 3, in which the
lubricant is present in an amount of 1 to 10 volume % of the total
powder particles, binder and lubricant.
11. A powder compaction method according to claim 10, in which the
binder and lubricant are present in an amount of 5 to 30 volume %
of the total powder particles, binder and lubricant.
12. A powder compaction method according to claim 3, in which the
binder and lubricant are present in an amount of 5 to 20 volume %
of the total powder particles, binder and lubricant.
13. A powder compaction method according to claim 2, wherein the
binder is selected from the group consisting of thermoplastic
resins, thermosetting resins, cyanoacrylate resins, polyvinyl
alcohol, ultraviolet hardening resins and resins which become
adhesive by the addition of water.
14. A powder compaction method according to claim 3, wherein the
lubricant is a metallic soap.
15. A powder compaction method, comprising: transferring an empty
mold to a first position; mounting a hopper onto the empty mold at
the first position; transferring the mold equipped with the hopper
to a second position at which a powder is filled into the hopper,
transferring the mold equipped with the hopper filled with the
powder to a third position; filling the powder into the mold at the
third position by air tapping; transferring the mold filled with
powder to a heat treatment apparatus; binding the particles of said
powder to each other without application of force from outside the
mold by a heat treatment in said heat treatment apparatus and
allowing the mold to cool to form a powder compact within the mold,
transferring the mold to a fourth position and attaching a suction
device to the powder compact within the mold; and removing the
powder compact from said mold with said suction device.
16. The powder compaction method of claim 15, wherein said heat
treatment apparatus is a high-frequency induction heater or a
microwave heater.
17. A powder compaction method for producing a green compact as an
intermediate for making a sintered final product, comprising:
filling a mixture of a powder and a binder into a mold by air
tapping, binding the particles of said powder to each other without
application of force from outside the mold after the mold is filled
with said powder to form a powder compact, driving the binder off
from said powder compact to form said green compact, and then
removing the green compact from said mold.
18. A powder compaction method according to claim 17, in which the
binding of the powder particles is carried out by heat treatment
within the mold.
19. A powder compaction method according to claim 17, in which the
binding of the powder particles is carried out by a chemical
reaction within the mold.
20. A powder compaction method according to claim 17, in which the
binder is present in an amount of 4 to 20 volume % of the powder
particles.
21. A powder compaction method according to claim 17, in which the
mixture further comprises a lubricant present in an amount of 0.5
to 14 volume % of the total powder particles, binder and
lubricant.
22. A powder compaction method according to claim 21, in which the
lubricant is present in an amount of 1 to 10 volume % of the total
powder particles, binder and lubricant.
23. A powder compaction method according to claim 22, in which the
binder and lubricant are present in an amount of 5 to 30 volume %
of the total powder particles, binder and lubricant.
24. A powder compaction method according to claim 22, in which the
binder and lubricant are present in an amount of 5 to 20 volume %
of the total powder particles, binder and lubricant.
25. A powder compaction method according to claim 17, wherein the
binder is selected from the group consisting of thermoplastic
resins, thermosetting resins, cyanoacrylate resins, polyvinyl
alcohol, ultraviolet hardening resins which become adhesive by the
addition of water.
26. A powder compaction method for producing a green compact as an
intermediate for making a sintered final product, comprising:
transferring an empty mold to a first position; mounting a hopper
onto the empty mold at the first position; transferring the mold
equipped with the hopper to a second position at which a mixture of
a powder and a binder is filled into the hopper; transferring the
mold equipped with the hopper filled with the mixture to a third
position; filling the mixture into the mold at the third position
by air tapping; transferring the mold filled with the mixture to a
heat treatment apparatus; binding the particles of said powder to
each other without application of force from outside the mold by a
heat treatment in said heat treatment in said heat treatment
apparatus and allowing the mold to cool to form a powder compact
within the mold, driving the binder off from said powder compact to
form said green compact, transferring the mold to a fourth position
and attaching a suction device to said green compact within the
mold; and removing said green compact from said mold with said
suction device.
27. The powder compaction method of claim 26, wherein said heat
treatment apparatus is a high-frequency induction heater or a
microwave heater.
Description
FIELD OF THE INVENTION
This invention relates to a powder compaction method. The powder
compacts obtained by such a method are subjected to a heat
treatment or sintering process, by which various kinds of parts
such as machine parts are produced.
BACKGROUND OF THE INVENTION
The following methods have been known as powder compaction methods:
(1) the die pressing method, in which a powder packed in a
cylindrical die is compressed with punches; (2) the cold isostatic
pressing (CIP) method, in which a powder packed in a rubber mold is
compressed by means of liquid; (3) the rubber isostatic pressing
(RIP) method disclosed in U.S. Pat. No. 5,250,255, in which a die
is loaded with a rubber mold filled with a powder, and then
compressed with punches; (4) the extrusion molding method, in which
a slurry of powder is extruded from the die; and (5) the metal
injection molding (MIM) or powder injection molding (PIM) method,
in which a mixture of a powder and binder is heated until the
binder has fluidity, and then injection molded. The metal injection
molding together with powder injection molding are hereinafter
referred to as "the PIM method".
The die pressing method cannot be applied to compaction of shapes
that are impossible to be pulled out of the die, and also pressing
long shapes such as tubes is difficult with this method. The CIP
method has problems in near-net-shape performance and productivity.
The RIP method is advantageous over those two methods above in
terms of flexibility of shapes and productivity, in that RIP
permits a wider selection of shapes and provides good
near-net-shape performance and productivity. However, the RIP
method is less flexible than the PIM method in terms of the
selection of shapes. The disadvantage of the PIM method is that it
uses a mixture of a powder and binder in which the quantity of the
binder reaches as much as 40 to 50 volume %. It takes a long time
to eliminate such a large amount of binder from the compact in the
"debinder process," and this makes it difficult to produce thick
and large parts. Carbon contamination during the debinder process
is also one of the problems of the PIM method.
SUMMARY OF THE INVENTION
This invention is intended to solve the problems described above
that the conventional powder compaction methods suffer, by
providing, first, a process in which a mold is filled with a powder
by air tapping, while the powder particles are bound with each
other without mechanical compaction or the application of force
from outside the mold to form a compact, and then the compact is
taken out from the mold, second, a process in which a binder is
added to the powder so that the powder particles are bound with
each other by the binder to form a compact, third, a process in
which a lubricant is added to the powder, and fourth, a process in
which the powder particles are bound with each other by means of
heating.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view in perspective of an embodiment of the compact
produced by the method of this invention.
FIG. 2 is a vertical sectional view of a mold unit used for molding
the compact shown in FIG. 1.
FIG. 3 is a top plan view of the mold unit shown in FIG. 2.
FIG. 4 is a vertical sectional view of a mold unit and a feeding
hopper used for shaping the compact shown in FIG. 1.
FIG. 5 is a vertical sectional view of a mold unit and feeding
hopper with a cover element used for shaping the compact shown in
FIG. 1.
FIG. 6 is a vertical sectional view of a mold unit filled with a
powder.
FIG. 7 is a vertical sectional view of a mold unit illustrating a
step for ejecting the compact.
FIG. 8 is a vertical sectional view of a mold unit illustrating the
ejection step following the step in FIG. 7.
FIG. 9 is a schematic view of the powder compaction process of this
invention.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a material selected from various kinds of
powders such as metal powders, ceramic powders, resin powders and
the like which are substantial constituents of the produced by
heating or sintering compacts (such powders are hereinafter
referred to as "the base powder") or a material comprising a
mixture of a base powder and a binder or lubricant is filled into a
cavity of a mold, and while the material is being packed in the
mold, a treatment such as heat treatment is applied without
application of force from outside the mold so that the base powder
particles are bound with each other, or the base powder particles
are bound with each other without application of force from outside
the mold through a binder. Other methods of binding the particles
together in the mold include the use of binders that coalesce the
particles through a chemical reaction, by partial sintering of the
particles in the mold or by means of a thermal diffusion treatment
of the powder in the mold. Subsequently, the powder compact in
which the base powder particles are bound with each other or the
base powder particles are bound with each other through a binder is
taken out from the mold. The powder compact is then subjected to a
heat treatment or sintering, thereby producing an end product such
as a machine part.
As described above, in this invention, a powder is filled into a
mold by air tapping, and then subjected to a treatment such as heat
treatment without application of force from outside the mold so
that the base powder particles are bound to each other or the base
powder particles are bound to each other through a binder, thereby
producing a powder compact.
The air tapping method disclosed in U.S. Pat. No. 5,725,816 is a
powder filling method invented by the present inventors in which a
powder is filled into a cavity or container in a short time, with a
homogeneous and high density. The disclosure of U.S. Pat. No.
5,725,816 is incorporated by reference fully into this
specification. As disclosed in U.S. Pat. No. 5,725,816, the air
tapping method is defined as a packing method comprising the steps
of supplying a material into a space comprising a space part to be
packed with the material and a space connecting with the space
part, and subjecting the space supplied with the material to an air
tapping process at least once in which the air-pressure inside the
space is switched from a low air-pressure state to a high
air-pressure state alternately, thereby packing the material into
the space part at a high packing-density. In a typical form of this
filling method, a powder feeding hopper loaded with a powder is
mounted upon the opening of a cavity, then first the air existing
in the hopper and cavity is evacuated, and then from the opening of
the cavity, air is introduced into the cavity through the feeding
hopper. The switching of air-evacuation to air-introduction is
carried out rapidly by operation of a high speed valve, and this
switching is repeated several times. The speed of the air flow is
high when the air flows from the feeding hopper toward the bottom
of the cavity, and low when the air flows reversibly. The powder in
the hopper is thus filled into the cavity with a high density.
Because this process is carried out with a sound resembling a
mechanical tapping while the powder is highly densified, it is
called "air tapping". The air tapping method can also be used for
filling a cavity with two openings. In this case, the feeding
hopper is mounted upon one of the two openings, and from another
opening, air in the feeding hopper and the cavity is evacuated.
Then the opening through which air is evacuated is closed, and air
is introduced rapidly from the top opening of the feeding hopper
into the cavity. This cycle comprising the air-evacuation followed
by the air-introduction is repeated several times so that the
powder is filled into the cavity with a high density.
In the form of air tapping explained above for use in the present
invention, the air in the spaces of the hopper and the cavity that
is at one atmosphere of pressure is first evacuated. This means
that the low air-pressure state is lower than one atmosphere. In
another form of this filling method, the low air-pressure state is
kept at one atmosphere, and the high-air pressure state is raised
to a pressure higher than one atmosphere. In such a case, the
air-introduction is carried out against the existing air-pressure
that is at one atmosphere at the beginning.
By means of this air tapping method, powders can be filled into a
cavity in a short time, homogeneously and to a high density. In
addition, cavities with complex shapes such as a cavity consisting
of several projecting parts can be thoroughly filled with powder
homogeneously and to a high density in all comers of the mold
cavities.
The present inventors determined that the above advantages of the
air tapping method could be utilized by adapting the RIP method.
After a powder is compressed by RIP and while the pressure was
decreased for taking out the compact from the cavity, the cavity is
restored to its original shape. However, during this restoration,
we found that the compact sometimes suffered from many cracks. Due
to this defect, the range of compressible shapes of the compact was
limited.
The present inventors then determined that the powder particles
filled into a cavity by the air tapping method could be bound to
each other by means other than pressing, and verified the
effectiveness of this method through repeated experiments. This
invention makes it possible to obtain powder compacts with complex
shapes with a minimum use of binders, of which PIM needs to use
much more.
The obtained powder compacts were then subjected to a heat
treatment, thereby producing parts with complex shapes with high
performance and high productivity.
We also found that an important technique for filling a powder
homogeneously and in a highly densified state into a cavity having
many projecting parts includes the addition of a lubricant to the
powder, so that the lubricated powder is smoothly transferred deep
into the cavity by the air flow. If the lubrication of the powder
is insufficient, the powder tends to stick in the division corners
of the mold, which may affect the performance of the present
invention. Except for powders such as Teflon powder having
lubrication themselves, lubricants or surfactants such as zinc
stearate should be added to the powder and stirred and mixed enough
so that the surfaces of the powder particles are covered with the
lubricant. By using such well-lubricated powders, even such
cavities with complex shapes having many projecting parts can be
filled with powder homogeneously and to a highly densified state.
The powder particles are then bound to each other and subjected to
a heat treatment or sintering, thereby producing machine parts or
the likes with high performance.
As the lubricant, any kind of surfactant such as metallic soaps,
waxes, greases can be used. However, in order to efficiently fill
the powder into the cavity by air tapping, the kind and quantity of
the lubricant should be determined so that the powder does not
agglomerate or have cohesiveness. The added lubricant is to be
eliminated together with the binder during the debinder process.
Therefore, preferably, solid lubricants such as metallic soaps,
e.g., zinc stearate, calcium stearate, barium stearate, aluminum
stearate, magnesium stearate and other such metallic soaps, rather
than liquid lubricants such as greases should be used as the
lubricant. The preferable quantity of the lubricant is 0.5-14
volume percent (vol %), and preferably, 1-10 vol %.
The mixing of the binder can be carried out in either way of the
following:
(1) A powder with a fusing point lower than that of the base powder
(hereinafter this powder is referred to as "the binder powder") is
mixed with the base powder, and the mixture is filled into a mold.
Once the mixture is filled into the mold, a heat treatment is
applied to the mixture so that only the binder powder is fused. The
base powder particles are bound with each other through the fused
binder powder. Then the mold is cooled and the powder compact is
taken out.
(2) The particle surfaces of the base powder are coated with the
binder. The binder-coated base powder is filled into a mold.
Subsequently, the filled base powder is subjected to an appropriate
treatment (such as a chemical treatment, light or thermal
diffusion) so that the base powder particles are bound with each
other through said binder, and then the powder compact is taken
out.
The material for the binder should have a fusing point lower than
that of the base powder. Resins are low fusing point good materials
for the binder, and both thermosetting resins and thermoplastic
resins can be used. However, in order to obtain sufficient bonding
force with minimum use of the binder, thermoplastic resins are more
preferable. Furthermore, as described later, when employing a means
other than heat treatments, instantaneous adhesives such as
cyanoacrylate, ultraviolet hardening resins and resins which become
adhesive by addition of water such as PVAs can be used being mixed
with the base powder, or as the material for coating the surfaces
of base powder particles.
In the present invention, the binder should only have sufficient
bonding force to bind the base powder particles to each other.
Therefore, the quantity of the binder to be blended does not need
to be so high as the 40-50 vol % that is needed in the PIM method,
but as low as 4-20 vol % is enough for the present invention. Even
when a lubricant is mixed, the total ratio of the binder and
lubricant may be as low as 5-30 vol %, and most of the time it is
adjustable to the range from 5 to 20 vol %. Because of the far
smaller quantity of binder than that used in PIM, it takes only
several hours to eliminate the binder in the present invention,
while the debinder process in PIM takes a few days. PIM cannot be
adopted for producing thick or large parts due to the large
quantity of the binder, which is as much as 40-50 vol %. When
producing thick and large parts by PIM, it takes a long time to
eliminate the binder, the elimination tends to be insufficient, or
compacts break due to swelling during the debinder process. Because
of the use of far less binder, the present invention allows such
thick and large parts to be produced without problems.
In the PIM method, compacts are produced from a mixture of a powder
and binder which is fused and subjected to pressure in an injection
molding device. Therefore, the die needs to be made of a metal with
a high strength, causing the die costs to swell. In addition,
because the compacts are produced by means of injection molding in
PIM, the flowability of the powder to be fused needs to be
increased by adding a binder as much as 40-50 vol %. In PIM, the
large quantity of the binder should be eliminated before sintering.
If the debinder process is carried out promptly at a high
temperature in this method, the compacts tend to deform or break.
To prevent such problems, it takes a few days or more to get
through the debinder process, which causes poor productivity in the
PIM method. In the present invention, the powder is directly filled
into a mold, and the quantity of the binder to be added is far less
than that in PIM. The time for the debinder process in the present
invention can therefore be as short as that in ordinary powder
compaction methods. In addition, because of the good flowability of
the powder, even cavities with complex shapes can be filled by air
tapping as well as by using a mold with a separated body. Because
the present invention can employ not only molds made of metals but
also molds made from materials which are easy to shape such as
synthetic resins, production of the molds is easy and cheap which
leads to largely reduced production costs.
Examples of the present invention are hereinafter explained in
which a mixture of a binder powder and a base powder is filled into
a mold to produce a compact C shown in FIG. 1 consisting of three
discs c1, c2 and c3 which are connected by two cylinders c4 and
c5.
As shown in FIGS. 2 and 3, a mold made of a hard synthetic resin,
metal or hard rubber is denoted by 1. The mold 1 is provided with a
cavity 2 for shaping the compact 1 in FIG. 1. The mold 1 has an
open top and projecting ring parts 1b and 1c to form the
cylindrical parts of the compact C, c4 and c5, respectively. In
order to take out the formed compact C from the mold 1, the mold 1
is separated along the center into two parts 1' and 1". The bottom
1d of parts 1'and 1"is provided with recesses 1e which are formed
as arcs having a radius smaller than that of outer periphery of the
mold 1.
Movable blocks 3 on which the separated mold parts 1' and 1" are
mounted are located at the bottom of the mold 1 properly spaced
from each other. The movable blocks 3 are provided with projecting
parts 3a which are to be inserted into the recesses 1e formed in
the bottom 1d, as well as with projecting parts 3b which have
surfaces contacting with an outer peripheral wall of the separated
mold parts 1' and 1".
A table element 4 is provided with a projection 4a to be inserted
into the space between the movable blocks 3, and a part of the
bottoms 1d of the separated mold parts 1' and 1" is mounted upon
the projection 4a. The movable blocks 3 are mounted on the table
element 4. The mold unit U comprises the mold 1 consisting of
separated mold parts 1' and 1", the pair of movable blocks 3, and
the table element 4.
Now the process of producing the compact C by using the mold unit U
mentioned above is described.
As shown in FIG. 4, a cylindrical hopper 5 is mounted on the top
surface of the mold 1. A grid element 5a is attached to the bottom
opening of the hopper 5. The grid element 5a may comprise wires
formed in parallel by a certain distance, or meshes of a certain
size or a thin metal plate punched to have a number of holes of
uniform size. The grid size (or distance between wires, mesh size,
or size of punched holes) is adjusted so that the powder mixture
(hereinafter simply referred to as the "powder") can pass through
the grid element 5a during air tapping, but cannot substantially
pass through when the powder is fed into the hopper 5 from a powder
feeder not shown in the drawing.
The hopper 5 is mounted on the top surface of the mold 1 of the
mold unit U. The hopper 5 is loaded with a powder p fed from a
powder feeder not shown in the figure. The quantity of the powder p
is naturally larger than that to be filled into the cavity 2, but
preferably it should be enough that after the powder p is filled
into the cavity 2 of the mold 1 by air tapping, there is still
quite a bit of powder p remaining in the hopper 5. It is also
possible to mount the hopper 5 preliminarily loaded with the powder
p on the top surface of the mold 1.
Subsequently, a cover element 6 provided with an air
evacuation/introduction pipe 6a is mounted onto the top opening of
the hopper 5 mounted on the top surface of the mold 1. Then by
means of a low and high-air pressure generator not shown in the
figure, the air inside the hopper 5 is evacuated through the air
evacuation/introduction pipe 6a so that the inside of the hopper 5
is brought into a low-air-pressure state. Subsequently, by the low
and high-air pressure generator, air is introduced rapidly into the
hopper 5 through the air evacuation/introduction pipe, so that the
inside of the hopper 5 is brought into a high-air-pressure state.
This cycle is repeated several times. Through this air tapping
process, the powder p loaded in the hopper 5 is filled into the
cavity 2 of the mold I through the grid element 5a. After the
cavity 2 of the mold 1 is filled with the powder p, the cover
element 6 is detached from the top opening of the hopper 5 which is
then dismounted from the mold 1 filled with the powder p, when the
powder p is divided into a portion filling the cavity 2 of the mold
1, and a portion remaining in the hopper 5.
In this example, the low-air pressure state is lower than one
atmosphere of pressure. However, as previously stated, air tapping
may be carried out in a pressure over one atmosphere when the low
air-pressure state is at one atmosphere and the high air-pressure
state is higher than one atmosphere.
Subsequently, the mold unit U filled with the powder p is put in
heat treatment equipment such as a furnace so that the powder p is
subjected to a heat treatment. The heat treatment temperature
should be too low to fuse the base powder but high enough to fuse
the binder powder. By such a heat treatment, liquid us resin
resulting from the fusing of the binder powder thoroughly fills the
spaces between the base powder particles. After heat treatment for
an appropriate time, the mold unit U is taken out from the heat
treatment equipment, and then cooled. The mold unit U may be cooled
naturally in a room temperature, or compulsory by applying a cooled
air.
As shown in FIG. 7, the powder compact C is then held with a
suction pad v1 which is attached to a vertically movable vacuum
suction device V1 placed on the compact C in the mold 1 driven by a
cylinder or the like although not shown. Before or after the
compact C is sucked by the vacuum suction device V1, suction pads
v2 are attached to the outer peripheral walls of the movable blocks
3, and by means of a vacuum suction device V2 which is driven by a
cylinder or the like not shown, the movable blocks 3 are sucked
with the suction pad v2.
Subsequently, by driving the vacuum suction device V2, movable
blocks 3 attached to the suction pad v2 are moved horizontally on
the table element 4 away from each other, by which the separated
mold parts 1' and 1" which are inserted in the recesses 1e provided
in the bottoms 1d are also moved horizontally away from each other.
After the ring parts 1b and 1c are pulled out of the clearances
formed between the disc parts c1.about.c3 of the compact C, the
driving of the vacuum suction device V2 is stopped so as to stop
the movement of the movable blocks 3. Then, the driving of the
vacuum suction device V1 is stopped, and the compact C sucked and
attached to the suction pad v1 is taken out from the mold 1 by
moving the compact C upward, or forward or backward relative to the
plane of FIG. 8.
The compact C taken out by means of the vacuum suction device is
then transferred to the debinder process to remove the binder
resin, i.e., fused binder powder. After the binder is eliminated,
the desired end product such as a machine part is obtained.
Meanwhile, the vacuum suction device V2 is driven again and the
movable blocks 3 sucked and held with the suction pads v2 are moved
reducing the distance between them so that the separated mold parts
1' and 1" are brought into contact. Then, by stopping the work of
the vacuum suction device, the movable blocks 3 are released from
the suction pads v2, and the vacuum suction device V2 is moved by
its driving mechanism so as to come to the standby position away
from the mold unit U.
FIG. 9 illustrates an example of the continuous production system
of powder compacts comprising the powder filling process in which
the powder p is filled into the cavity 2 of the mold 1 through the
hopper 5, the air tapping process, the heat treatment process to
which the mold unit U comprising the mold 1 filled with the powder
p is subjected, and the ejecting process in which the powder
compact is taken out from the mold 1 of the mold unit U.
The mold unit U containing mold 1 of which cavity is not filled
with powder p is placed on conveyer equipment T which comprises a
conveyer belt or roller conveyer constantly or intermittently
moving by which the mold unit U is transferred to the right
direction in FIG. 9 (Step I). In the example of FIG. 9, a roller
conveyer t1 is shown as the conveyer equipment T which is driven by
a driving mechanism not shown in the figure.
Subsequently, a stopper S1 is forwarded into the transfer line of
the mold unit U being transferred to the right by the roller
conveyer t1 so that the mold unit U is stopped upon contacting the
stopper S1. With the mold unit U being stopped, by an automated
machine such as a robot, the hopper 5 is mounted on the mold 1 of
the mold unit U (Step II).
The stopper S1 is then withdrawn from the transfer line of the mold
unit U and the mold unit U is again carried by the conveyer
equipment T. After that, a stopper S2 is forwarded into the
transfer line of the mold unit U so as to stop the mold unit U at
the position provided with the powder feeder A by which the powder
is poured into the hopper 5 (Step III).
Subsequently, the stopper S2 is withdrawn from the transfer line of
the mold unit U, and the mold unit U on which the hopper 5 is
mounted is transferred to the position of the air tapping process,
when the stopper S3 is forwarded to stop the mold unit U (Step
IV).
Then, the top opening of the hopper 5 is covered with a cover
element 6 provided with the air evacuation/introduction pipe 6a,
and air tapping is carried out to fill the powder p in the hopper 5
into the cavity 2 of the mold 1 through the grid element 5a. After
the cavity 2 is filled with the powder p, the cover element 6 and
hopper 5 are dismounted. Or, the hopper 5 may be dismounted at the
next stage.
The stopper S3 is then withdrawn from the transfer line of the mold
unit U, the mold unit U with the cavity 2 of the mold 1 filled with
powder p is carried into heat treatment equipment H formed as a
tunnel (Step V), where the binder powder is fused to be a liquidus
resin that thoroughly fills the spaces between the base powder
particles.
The mold unit U after exiting the heat treatment equipment H is
naturally or force-cooled. Then a stopper S4 is forwarded to
contact the mold unit U. When the mold unit U stops, the suction
pad v1 of the vacuum suction device V is attached to the top
surface of the compact C in the mold 1, and the suction pads v2 of
the vacuum suction device V2 are attached to the movable blocks 3
as well (Step VI).
Then by driving the vacuum suction device V2, the separated mold
parts 1' and 1" are moved away from each other, and the ring parts
of the mold 1, 1b and 1c are ejected from the clearances between
the disc parts c1.about.c3. The driving mechanism of the vacuum
suction device V2 is then stopped to stop the transferring of the
movable blocks 3, when the vacuum suction device V1 is driven to
suck and hold the compact C with the suction pad v1 and the compact
C is taken out from the mold 1.
By working the driving mechanism for the vacuum suction device V2,
the movable blocks 3 sucked and held with the suction pad v2 of the
vacuum suction device V2 are moved close to each other so that the
separated mold parts 1' and 1" are brought into contact. Then the
vacuum suction device V2 is stopped so as to release the movable
blocks 3 from the suction pad v2, and the vacuum suction device V2
is driven by the driving mechanism to move away from the mold unit
U to its standby position (Step VII). The mold unit U from which
the compact C is ejected now comprising the separated mold parts 1'
and 1" in contact with each other is brought back to Step I in FIG.
9, while the ejected compact C is transferred to the debinder
process so that the binder resin contained in the compact C is
eliminated. After this debinder process, the desired end products
such as machine parts are obtained. In the above described example,
the mold 1 comprises two separated mold parts 1' and 1" and is held
by a pair of movable blocks 3 and a table element 4. However, in
another embodiment, the mold 1 may be held by a table provided with
recesses into which the lower part of the mold 1 can be inserted.
It is also possible to construct the mold unit by binding the
separated mold parts 1' and 1" with a band or some other structure
to prevent them from separating. In the case of using a mold 1
comprising one body, it is of course unnecessary to install such a
holding means.
The dimensions of the compact C which is shown in FIG. 1 and
produced in the above example were as follows: The disk parts
c1.about.c3 were 40 mm in diameter and 10 mm in thickness, and the
cylinder parts c4 and c5 are 20 mm in diameter and 10 mm in length.
The base powder used was a ferrite powder with average particle
size of 50 .mu.m and 90 vol % in quantity. The powder used as a
binder powder was an epoxy resin powder with a fusing point of
65.degree. C. and 8 vol % in quantity. As the lubricant, 2 vol %
magnesium stearate was added. The ferrite powder, epoxy resin
powder and magnesium stearate were well mixed in a rocking
mixer.
The compact C in FIG. 1 was produced using the above powder mixture
by the above described compaction method. The compacts taken out
from the separated mold parts 1' and 1" had no cracks nor chipping,
as well as they were strong enough to endure any handling in the
transfer line and debinder process or in other processes. The time
consumed for elimination of the binder was about two hours, which
was far less than the debinder time needed in MIM and PIM.
In the example explained above, a powder mixture containing at
least a base powder and a binder powder was used. In another case,
it is also possible to apply a resin coating to the base powder,
and to fill the resin-coated base powder into a mold which is then
subjected to a heat treatment so that the resin is fused to bind
the powder particles with each other. In this case, thermoplastic
resins are preferred to thermosetting rezins.
As a means for the heat treatment, high-frequency heating may be
employed instead of the furnace in the above example. As the
high-frequency heating means, a high-frequency induction heating
unit utilizing the heat generation of a magnetic material effected
by the hysteresis loss and the Joule effect of eddy currents in a
high-frequency magnetic field of 300K.about.3 Mz, and a
high-frequency induction heating or microwave heating used in
microwave ovens utilizing the heat generation of a dielectric due
to the dielectric loss in a high frequency of 3.about.30 MHz can be
used.
In the example above, a mixture containing at least a base powder
and a binder powder is filled into a cavity of a mold, and then the
powder filled mold is subjected to a heat treatment at a
temperature high enough to fuse the binder powder but too low to
fuse the base powder, thereby fusing the binder powder so that the
base powder particles are bound with each other through the fused
binder powder. This process may be carried out as described below
so that the obtained compact does not suffer cracks or chipping,
thus retaining its shape for easy handling.
A base powder containing no water is coated with an instant
adhesive which works as a binder and hardens by absorbing humidity,
and the coated base powder is filled into a mold in an atmosphere
with very low humidity. Subsequently, a gas containing water (air
or N.sub.2 gas) is introduced into the base powder in a mold so
that the instant adhesive coating the base powder is hardened,
thereby binding the base powder particles with each other so as to
retain the shape of the obtained compact.
In another case, an adhesive which hardens when receiving
ultraviolet rays may be used as a binder. The base powder is coated
with such an adhesive, and the coated base powder is filled into a
mold made of a transparent material through which ultraviolet rays
can pass. Then ultraviolet rays are applied to the mold filled with
said base powder so that the adhesive is hardened and binds the
base powder particles with each other, thereby retaining the shape
of the obtained compact.
Or, a material such as PVA (polyvinyl alcohol) that exerts its
bonding force when containing water can also be used as the binder.
Such a material in the form of powder is mixed with the base
powder. The mixture of the base powder and said material that is to
have bonding force when containing water is kept dry and filled
into a mold. Subsequently, water is blown into the powder mixture
so that the binder material gets to have a bonding force by which
the base powder particles are bound with each other.
The process may also be carried out without using binders but only
a base powder. After the base powder is filled into a mold, it is
subjected to a heat treatment to a degree by which the base powder
is slightly sintered or deposited so that the base powder particles
are bound with each other, thereby producing a powder compact.
However, if the base powder filled into a mold is heated to a too
high temperature, the powder that is excessively sintered or fused
causes the compact to break, and the desired product cannot be
obtained.
When constructed as described above, the present invention has the
following advantageous effects. The variety of shapes of the
compact is far wider in this invention than in other conventional
methods, and net shape manufacturing of products with complex
shapes is made possible by this invention. Because the present
invention uses far less binder compared to MIM and PIM that are
expected as methods for producing products with complicated shapes,
the time needed for debinder is much shorter than in MIM and PIM,
which require too long time for elimination of the binder. The
productivity is therefore improved in the present invention. The
present invention has made it possible to produce large products or
thick products with complex shapes that have been difficult to
produce by MIM and PIM due to the difficulty of elimination of the
large quantity of binders.
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